There is a reason experienced Medicare brokers keep a calendar on their desk. Medicare has three election windows, AEP, OEP, and plan-specific SEPs, and each one permits a different set of transactions. Telling a client they can make a change when the calendar says otherwise is one of the more damaging errors in this vertical. The AEP is the one window that opens everything; OEP is significantly narrower than most clients assume; and SEPs are event-driven, not time-driven.
Key Takeaways
- AEP (Oct 15 to Dec 7) is the only window that opens all plan-type changes, including moving between MA and Original Medicare plus Medigap.
- OEP (Jan 1 to Mar 31) allows exactly one transaction: an MA enrollee can switch MA plans or disenroll to Original Medicare. No new Medigap enrollment through this window.
- Medicare Advantage SEPs are triggered by specific qualifying events defined in 42 CFR 422.62 and CMS guidance, not by calendar period alone.
- The 5-star SEP runs continuously from December 8 through November 30 of the following year and requires a 5-star rated MA plan to be available in the county.
- Part D late enrollment penalties accumulate at 1 percent of the national base beneficiary premium per month without creditable coverage, even if the gap occurred because a client missed a window.
Annual Enrollment Period (AEP): October 15 to December 7
AEP is the broadest Medicare election window. During those 54 days, a beneficiary can make any plan change: move from Original Medicare to a Medicare Advantage plan, leave MA to return to Original Medicare, switch between MA plans, enroll in or change a Part D Prescription Drug Plan, or drop Part D coverage entirely. Plans elected during AEP take effect January 1 of the following year.
For brokers, AEP is the primary revenue window. Most of the year-round book-of-business work builds toward November and December. Quotit, Connecture, and other quoting platforms release their updated 2027 plan data in October alongside CMS publishing the Annual Notice of Change (ANOC) carriers must send to existing enrollees. A client who receives their ANOC and sees a premium increase, formulary change, or network reduction has AEP as the window to respond. The response must be submitted to the carrier by December 7; calls on December 8 will not be processed under the prior AEP.
One detail that catches clients off-guard: a beneficiary who switches plans multiple times during AEP is bound by the last election submitted before December 7. The window allows changes, and the last change wins.
Open Enrollment Period (OEP): January 1 to March 31
OEP was created by the Bipartisan Budget Act of 2018 to replace the prior Medicare Advantage Disenrollment Period and provide a more meaningful correction window. The key word in every OEP conversation is restricted. OEP allows one transaction: a Medicare Advantage enrollee can switch to a different MA plan or disenroll from MA to return to Original Medicare. That is the full scope.
What OEP does not allow:
- A beneficiary on Original Medicare cannot use OEP to join a MA plan.
- No Medigap enrollments or changes.
- No standalone PDP enrollments unless a client is disenrolling from an integrated MA-PD plan, which triggers a SEP for Part D separately.
- Only one plan change per OEP. The window does not allow multiple elections.
Plans elected during OEP take effect the first of the month after the enrollment is received by the carrier.
Medicare Advantage SEPs: event-driven, not calendar-driven
SEPs for Medicare Advantage operate on a different logic than AEP and OEP. CMS codifies qualifying events in 42 CFR 422.62(b) and supplemental subregulatory guidance. The triggering event, not the date on the calendar, is what opens the window. SEP windows are typically 60 days from the qualifying event, though some are 30 days.
Common MA SEPs a broker will encounter:
| SEP type | Qualifying event | Window |
|---|---|---|
| Change of residence | Moving permanently out of plan service area | 60 days before or after the move |
| Loss of employer/union coverage | Involuntary loss of creditable coverage | 60 days after coverage ends |
| Medicaid status change | Gaining or losing Medicaid or Extra Help (LIS) | 60 days from the effective date of the change |
| Long-term care | Moving into or out of a SNF, nursing facility, or LTC | 60 days from the move date |
| 5-star SEP | 5-star rated MA plan available in county | Dec 8 through Nov 30 of the following year; one use per year |
| Plan termination | MA plan exits county or terminates | 60 days before or after plan termination date |
Illustrative examples. SEP eligibility is determined by CMS and the plan at the time of the qualifying event. Confirm the specific triggering event in the applicable CMS guidance before advising a client to submit an election.
The 5-star SEP: the one that resets every year
The 5-star SEP is structurally different from every other SEP because it is not triggered by a life event. CMS releases MA plan Star Ratings each fall (typically October), and the 5-star SEP for those newly rated plans opens December 8 of that year and runs through November 30 of the following year. During that window, any Medicare beneficiary enrolled in a lower-rated MA plan can switch to the 5-star plan once, if one exists in their county.
The practical constraint: not every county has a 5-star rated MA plan. CMS publishes the current 5-star plan list on Medicare.gov. Brokers should verify county availability before mentioning this SEP to a client, because the disappointment of learning no 5-star option exists locally is avoidable.
The rating also resets. A plan with 5 stars in one year may drop to 4 stars in the next release, closing that SEP and opening a new one only for whatever plan earns 5 stars in the new cycle.
What each window does not cover: the table that matters
The fastest way to misadvise a client is to assume one window does what another does. The non-obvious exclusions:
- OEP does not allow Original Medicare beneficiaries to join MA.
- AEP does not govern Medigap. A client asking to change a Medigap plan during AEP will need to use medical underwriting in most states, regardless of what the calendar says.
- OEP and AEP do not restart the Medigap 6-month guaranteed issue window. That window is tied to Part B enrollment, not to these election periods.
- A client who disenrolls from MA during OEP and wants Part D coverage must enroll in a standalone PDP using the SEP triggered by that disenrollment. It does not happen automatically.
For the mechanics of Medicare Part B late enrollment penalties that accumulate when clients miss their enrollment windows, the Medicare Initial Enrollment Period 7-month window guide covers the IEP structure and penalty clock in detail. For clients facing IRMAA surcharges from prior income, the Medicare IRMAA explained guide covers the 2-year income lookback and the Form SSA-44 appeal process.
Frequently asked questions about Medicare enrollment windows
The questions brokers encounter most often when clients call about plan changes outside AEP.
What is the difference between Medicare AEP and OEP?
The Annual Enrollment Period (AEP) runs October 15 through December 7 and allows beneficiaries to make any Medicare plan change: switching between Original Medicare and Medicare Advantage, changing MA plans, enrolling in or changing a Part D prescription drug plan, or dropping MA entirely. The Open Enrollment Period (OEP) runs January 1 through March 31 and is significantly more restricted. During OEP, a beneficiary who is already enrolled in a Medicare Advantage plan can switch to a different MA plan or disenroll to Original Medicare. Beneficiaries on Original Medicare cannot use OEP to join a MA plan, and no one can use OEP to make a Medigap enrollment or change. Plans elected during OEP take effect the first day of the month after the enrollment is received.
Can a client enroll in a Medicare Supplement during OEP?
No. OEP applies only to Medicare Advantage plans. Medigap (Medicare Supplement) enrollment follows a different set of rules entirely. The guaranteed issue window for Medigap is the 6-month period beginning the month a beneficiary is both 65 or older and enrolled in Medicare Part B. Outside that 6-month window, Medigap insurers in most states can use medical underwriting to decline applicants or charge higher premiums. Some states have birthday rules (California, Illinois, Missouri, Nevada, Oregon, and a few others) that allow a limited window annually, but those are state law variations and do not apply in most states. A broker who advises a client to delay Medigap enrollment because OEP will be available is giving incorrect guidance.
What qualifies as a Medicare Advantage SEP?
CMS recognizes more than 20 qualifying events that trigger an MA SEP. The most common ones a broker encounters are: moving out of the plan's service area, losing employer coverage or Medicaid, gaining or losing Extra Help (Low Income Subsidy), residing in or moving into a long-term care facility, and plan termination or significant benefit change. The 5-star SEP is a special case: it runs continuously from December 8 through November 30 of the following year and allows any beneficiary to switch to a 5-star rated MA plan once per calendar year if one is available in their county. A 5-star plan designation is based on the prior year CMS Star Rating, which is released each fall. A plan that had 5 stars one year may not have them the next, so the SEP availability resets annually.
If a client drops MA during OEP, do they automatically get Part D coverage?
No. A client who disenrolls from an integrated MA-PD plan during OEP and returns to Original Medicare does not automatically receive Part D drug coverage. They must separately enroll in a standalone Prescription Drug Plan (PDP). The disenrollment from MA triggers a SEP to join a PDP, but the client must actively complete that enrollment. If they miss it or delay, any months without creditable drug coverage count toward the Part D late enrollment penalty, which is calculated at 1 percent of the national base beneficiary premium per full uncovered month. For 2026, CMS set the national base beneficiary premium at $36.78, making each penalty month approximately $0.37 in permanent monthly surcharge on future Part D premiums. The penalty compounds over time and has no cap.
Does the Medicare AEP apply to Medicare Supplement plans?
AEP does not govern Medigap. AEP is an election period specific to Medicare Advantage and Part D prescription drug plans. Medigap plans are issued by private insurers under state insurance law, and their enrollment rules are set by state regulations and the 6-month guaranteed issue window tied to Part B enrollment. A beneficiary with a Medigap plan does not need to take any action during AEP unless they also want to change a Part D standalone plan. A beneficiary who wants to switch Medigap plans outside the guaranteed issue window must apply and qualify through medical underwriting in most states. Some brokers conflate the two systems because both involve supplemental coverage, but their enrollment mechanics are entirely separate.
